RC Question 16 Explanation, by LSATHacks
DISCUSSION: Main point answers must first be true. All four wrong answers are either contradicted by the passage, or totally unsupported by the passage.
___________
- The passage isn’t talking about how the entire ocean floor formed. It’s about why the ocean floor has polarity, and how this explains the alternating magnetic strips around the mid-ocean ridge.
- This contradicts the passage. The first paragraphs says it was long known that basalt had magnetic properties.
- CORRECT. The two discoveries are: magnetic variations and the mid-ocean ridge (lines 5-6 and lines 26-30). This led to the theory in lines 33-40, and the justification in paragraph 3.
- Lines 9-11 mention local distortions on land. The passage doesn’t mention local compass distortions underwater. Totally irrelevant answer.
- The passage doesn’t say why the ocean floor was mapped in the 1950s. This answer combines two unrelated ideas from the passage.
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I’m a little lost with your explanation for eliminating option B here: Option B makes no claim that the entire ocean floor doesn’t have magnetic striping. I eliminated B because of it strangely focused on basalt & it’s magnetic properties. They were already aware of certain properties of basalt (lines 6-11). I understood the discovery more-so to be the odd variations found on the ocean floor (lines 5-6).
You’re right, thanks, this was a misread on my part. I’ve updated the explanation.
Note: This is an old comment but I wanted to address the comment.